Sample Band Program,
Here's a sample six week run using bands on a leg press. The trick is to gradually increase the band tension every two weeks. On all weeks, do sets of eight while ramping the weight until you reach a load you can barely get eight reps with, then stop.

Week 4-5: One set of pro-minis (long red Elite FTS bands)
Week 6-7: One set of monster-minis (long black EliteFTS bands)
Week 8-9: One pro-mini and one monster-mini per side
You could also alternate weeks like this:

Week 1 and 3: One set of pro-minis
Week 5 and 7: One set of monster-minis
Week 9 and 11: One pro-mini and one monster-mini per side

Chains
The same logic can be applied to chains. Here's a sample squat program – it assumes that you're an experienced lifter that's been around the block. On all weeks, do sets of six while ramping the weight until you reach a load you can barely get six reps with, then stop.

As for when to add the chains, I like to work up to a set weight and then just start adding chains – but no more weight.

Weeks 4 and 5: Two sets of chains (One for intermediate lifters)
Weeks 6 and 7: Four sets of chains (Two for intermediate lifters)
Weeks 8 and 9: Six sets of chains (Three for intermediate lifters)

The Lightened Method
No discussion of bands would be complete without mentioning the lightened method, or "reverse banding." Earlier I noted how bands add eccentric overload and pull the bar down towards you. The lightened method is just the opposite.

Take the bench press, for example. Instead of attaching the bands from the bottom of a power rack, you'd attach bands from the top of the rack. This way, when you lower the weight, the bands help you lift the weight off your chest. But as the weight comes up, the bands get slack and don't help as much near the top.

Remember, we're stronger during certain parts of an exercise, so we're limited by whatever our weak point is in a given range of motion. In the bench press, which has an ascending strength curve, we can lock out significantly more than we can budge off our chest.

So if you can bench 300 pounds for six reps, you can likely lock out 380 pounds for six reps – and attaching bands can simulate this. Put 420 pounds on the bar and the bands will make it feel like 300 pounds coming off your chest, but as you lift they'll get slack, so in effect, you lock out about 380 pounds.

Another reason I like reverse banding is safety. You can simulate lighter loads in the positions where you're most vulnerable to injury, such as the bottom position of the bench press, but still have heavier loads after you pass the danger zone.